Transition from Uni-Directional to Bi-Directional Distribution Grids

This report summarizes the outcome of the International Energy Agency (IEA) Photovoltaic Power Systems Programme (PVPS) Task 14 Subtask 2 activities with regard to high PV penetration in local distribution grids. The focus of this report is set on discussing technical PV integration issues in distribution grids - spanning high voltage, medium voltage and low voltage levels - of interconnected electric power systems and presenting solutions for the transition from uni- to bi-directional distribution grids. The recommendations are based on a case-study collection of best-practice examples provided by Subtask 2 participating countries.

The report is divided into three major sections. The section "Directional Distribution Gridsoperator's perspective which will occur along the way towards PV as a major electricity source in national power systems. A simple three-stage model is used to allocate technical challenges for grid operators to different national PV penetration scenarios.

The section "Bi-Directional Distribution Gridssolutions for an improved distribution grid integration of PV with respect to different PV penetration scenarios. Besides improved functionalities for smart PV inverters also novel assets for distribution system operators are discussed. Cost-benefit analyses highlight the significant economic potential of these solutions for reducing the overall costs of PV grid integration. Recommendations for a successful transition from uni- to bi-directional distribution grids are given based on the outcome of Subtask 2 and the experience of the Subtask 2 contributors in this field.

The final section discusses the national PV penetration scenarios, PV generation and demand, the provision of ancillary services by PV and the future interaction of smart girds, smart markets and smart inverters are discussed and current trends in research and development are highlighted.